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Inspired by this comment

Assume that a particularly deranged moustache-twirling villain with way more time and resources than is reasonable decides to build a satellite-launching rocket using chlorine trifluoride. (Never let your moustache-twirling villains get bored.)

Assume the ever-so-trivial engineering problem of actually building and launching the thing has been solved. Somehow.

With any choice of propellant, as long as it isn't even less usable than chlorine trifluoride (arguably an easy criterion, as long as you aren't using pre-mixed methane-oxygen), what could, at best, be its performances? How would its Isp and thrust compare to sane engines?

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Apparently Rocketdyne was employing particularly deranged moustache-twirling villains from the late '50s on, because they experimented with ClF3 combined with hydrazine, UDMH, and kerosene.

According to Astronautix, a vacuum specific impulse of 338 seconds using ClF3 and hydrazine was achieved, which isn't bad, but not out of reach of non-toxic modern methane/LOX engines.

The table here indicates that chlorine trifluoride doesn't yield significantly better specific impulse with hydrazine-family fuels than N2O4 does.

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  • $\begingroup$ experimented... notionally, no doubt. $\endgroup$
    – uhoh
    Apr 9, 2019 at 17:14
  • $\begingroup$ Rather alarmingly, in the book Ignition!, they experimented with ClF3 quite a lot. And that's possibly not the worst thing they considered using (The worst being a fuel doped with methyl mercury) $\endgroup$
    – Ingolifs
    Apr 9, 2019 at 19:50
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    $\begingroup$ As I recall, the real benefit in ClF3 was not in its mass specific impulse but it's volumetric. Whole lot of oxidizing power per gallon, which means smaller tanks. $\endgroup$
    – Tristan
    Apr 10, 2019 at 1:49
  • $\begingroup$ @Tristan Ah, good point. According to the linked table, the bulk density of ClF3 with hydrazine is about 1.5 instead of 1.07 for hydrazine/LOX or 1.2 for hydrazine/NTO. $\endgroup$ Apr 10, 2019 at 2:02
  • $\begingroup$ They did what? Well at least they didn't go full Captain Planet villain and actually launch rockets fueled with those horrors, right? $\endgroup$
    – Eth
    Apr 10, 2019 at 15:49

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